Model organisms have contributed significantly to the understanding of basic biological phenomena. Suitable animal models are at hand for some research disciplines like genetics, development and cell biology but are still sought after for others like epigenetics. Research of the last years has revealed that the marbled crayfish (Marmorkrebs), which was discovered in the mid-1990s, meets researchers' demands for a vigorous, genetically identical and eurytopic laboratory model very well. Its most prominent advantages are production of high numbers of genetically identical offspring, stepwise alteration of the phenotype by moulting, complex morphology and behaviour and sequential generation of segments and limbs. This paper first reviews the discovery and research history of the marbled crayfish, its biology and culture and its special advantages. It then discusses, based on the published data, its suitability as a laboratory model for various research disciplines. The greatest potential of the marbled crayfish lies in epigenetics and environmental epigenomics and in stem cell research and regeneration. The marbled crayfish also appears to be suitable for the investigation of the role of stochastic developmental variation and epigenetic inheritance in evolution and to contribute to evo-devo and eco-devo. This unique crayfish is even of some value for applied biologists, for example as a toxicological test species.

26 August 2008

Back in the 1960s, there was a lot of research interest in little flatworms, Planaria. They were being used as model organisms in research on learning and memory.

On the face of it, Planaria shared many advantages with other model organisms: it's small, easy to look after, and common. The field had its own journal, The Worm Runner's Digest, (later the Journal of Biological Psychology).

But I suspect you'd be hard pressed to find anyone using Planaria today as a general model organism. Indeed, there's a book titled, Whatever happened to Planaria? So why did Planaria fail as a model organism? I will confess to not having read the book above, but I can see a few reasons.

First, a major finding based on Planaria was... well.. weird. Basically, if you taught one animal something (like running a maze), then killed it and fed the pieces to another animal, it performed better at the task than expected. Much was written about this, and I think the bottom line is that it didn't replicate well. It didn't lead to useful experiments in other species. In some sense, this one claim may have discredited the field.

Second, as a model for learning and memory, Planaria were being studied just at a time when electrophysiology started to make huge progress in understanding the neural basis of learning. And here, Planaria are not convenient: they and their neurons are a bit small for electrophysiology. The sea slug Aplysia, on the other hand, had huge nuerons, and it filled the niche of a simple invertebrate model for studying learning.

Third, I can't help shake the impression that the field was somewhat insular. Maybe this is just an impression I get from The Worm Runner's Digest, at least. I don't know where a lot of other Planaria research at that time was published. This is the downside of having specialty journals on one organism: other people don't read it. If you're going to have a model organism, this is lethal.

To this day, though, The Worm Runner's Digest is justly remembered for its irreverent humour.

Pigeons have been the subject of several major biological research programs. Perhaps most famously, Charles Darwin talks at some length about pigeons and pigeon fanciers in On the Origin of Species. Fancy pigeons interested Darwin because they came in so many forms, yet were all descended from a common rock dove. If a few breeders with a few generations could cause such changes in form, imagine what Nature could do with vastly more time, Darwin argued.

Pigeons were also used in many key learning experiments by B.F. Skinner. Superdove talks about one of the stranger applications of this -- a proposed pigeon guided missile -- but the weirdness of that should not distract from how much they taught Skinner about learning mechanisms.

Then there's a branch of research about animal navigation, and clearly homing pigeons have contributed large amounts of knowledge there.

Yet despite these significant contributions, pigeons are not really considered a standard model organism in science today. Arguably, they could have been. But today, arguably the most prominent model organisms for animals are the fruit fly species Drosophila melanogaster, the mouse species Mus musculus, and the nematode worm species Caenorhabditis elegans. For plants, it's Arabiopsis thaliana.

Why did these win and pigeons not? The big four listed above were all model organisms for genetics. They were among the first to have a complete genome sequenced. And with the rise of molecular biology, that is a tremendous facilitator for research.

If Marmorkrebs have any hope of becoming a model organism for researchers, there needs to be a crayfish genome project.

18 August 2008

11 August 2008

Although I haven't been blogging a huge amount, there's actually been a fair amount of stuff I've been doing behind the scenes, as it were.

In one of those little coincidences, Marmorkrebs have suddenly become the topic of conversation on several different pet discussion forums (see here and here). I've been sticking my head in to provide what information I can, and particularly to suggest that anyone who wants to keep these be careful about it.

Again, I would ask that anyone who is a hobbyist with Marmorkrebs to email me. I just want to get a sense of when they made it into North America in the pet trade.

I also made a few little updates to the main page. In particular, I highlighted two new articles, one of which I just got this morning. I list articles "in press" on the home page before they show up in the blog. I publish abstracts on the blog when they have their final volume, page number, and so on.